Fix a potential corruption in release_input_thread().

If the media instance owns the input and libvlc_media_instance_release()
is called immediately after libvlc_media_instance_stop(), there is a
chance that we try to free the input resources before the thread is
effectively terminated. To avoid this, we call input_DestroyThread()
instead of vlc_object_release() at the end of release_input_thread() when
the media instance owns the input thread.

src/control/media_instance.c

@@ -92,11 +92,12 @@ static void release_input_thread( libvlc_media_instance_t *p_mi )
 
         /* We owned this one */
         input_StopThread( p_input_thread );
+        input_DestroyThread( p_input_thread );
 
         var_Destroy( p_input_thread, "drawable" );
     }
-
-    vlc_object_release( p_input_thread );
+    else
+        vlc_object_release( p_input_thread );
 
     p_mi->p_input_thread = NULL;
 }